In many applications it is desirable to track, in a non-contact manner, the position of an object as it moves through 3-dimensional space. One method of accomplishing this is to embed an RF transmitter in the object to be tracked. Multiple RF receivers, positioned at known locations, capture the transmitted signal from the object to be tracked. Because the RF energy propagates at a known velocity, the differences in arrival time of the signal at any one pair of the receivers can be used to determine the possible positions of the tracked object in two dimensions.
If the above is carried out using several pairs of receivers, the object's position can be determined in three dimensions. A minimal setup for 3D object tracking utilizes four receivers, one that serves as a common reference for each of the other three receivers. By measuring the time difference of arrival of the signal at each of these three pairs, the resulting system of 3 equations and 3 unknowns (x, y, z coordinates) can be solved and the object's position determined.
Several problems may occur with this type of system. First, nearby sources of RF energy may interfere with the clean reception of the tracked object's RF transmission. Second, RF energy transmitted by the object to be tracked may reflect off of interfering surfaces and generate echo signals which may be received by the receiver and distort the true, direct path arrival time. The latter issue is know as multipath interference and may reduce system accuracy. It is desirable to develop methods to overcome the effects of multipath interference and maintain system accuracy.